632 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



Alden crusher. — The Aldeu crui-ber and pulverizer, is uot in use at suielters, wbicli, 

 wben they have any pulverizing to do, use Cornish rolls ; but it is used at the samp- 

 ling works, where a considerable amount of pulverizing is done. The jaws of this 

 crusher differ essentially from those of the others in this respect — that their grooves 

 are perpendicular to the length of the jaws, while in the others these grooves are par- 

 allel to the length. 



Fig. 1, Plate XLV, gives a perspective view of the Alden crusher, in which 

 portions of the jaws and jaw-faces are shown in section. The jaws are hung upon 

 wroughtiron trunnions, the ends of which project through and are supported by the 

 sides of the frame. Motion is imparted by linlcs connected with the trunnion ends, 

 and driven by studs projecting from a sliding yoke beneath. This yoke is connected 

 with a crank-shaft by a pitman. The rotation of the crank moves the yoke to and fro 

 on a nearly horizontal plane, alternately moving and pushing the movable ends of the 

 two jaws, and imparting a rubbing motion, which is the main feature of the machine. 

 The jaws may be adjusted at varying distances, so as to obtain a product of varying 

 degrees of fineness. 



The Cornish rolls, used by both the smelters and samplers for grinding their 

 samples, consist of two steel cylinders, VI inches long and C inches in diameter, con- 

 nected by cog-wheels, driven by pulley and transmission belt, and fed by means of a 

 thin sheet-iron funnel, having the shape of an inverted truncated pyramid. These 

 rolls are usually set one-eighth of an inch apart. 



ASSAYING. 



In LeadviUe assaying is quite au important branch of the miuing and smelting 

 industries. In addition to the assayers attached to all the smelting and sampling 

 works and to the principal mines, there are no less than twenty independent assayers 

 residing in the city and having their own assay olBces. Besides being employed as 

 referees and experts in cases of dispute between mines and smelting works, the latter 

 are patronized by the prospectors and small miners. 



The chief assays made in the camp are silver, gold, lead, iron, and gangue assays, 

 and at some smelters specitic-gravity determinations of slags. 



Furnaces The laboratories are generally jjrovided with permanent crucible and 



muffle furnaces, made of common brick, lined with Are brick, and placed side by side, 

 as is shown in Plate XXXIX ; but very often the two furnaces are separate. 



By means of the dampers D' and D' in the chimney, the assayer can regulate the 

 draft and the intensity of heat in the furnaces. The apertures A B C D are closed 

 by means of sheet-iron plates, easily removed by tongs. Occasionally, portable clay 

 furnaces, of American and English manufacture, are used for cupellation. 



Pulverization The ores and slags are, first of all, coarsely pounded in a cast-iron 



mortar (Fig. 12, Plate XLIII), a form of mortar that is not well adapted for this use, 

 since it is too thin and very often breaks before the stone does. The coarsely pounded 

 material is then ground on the buck plate. This consists of a cast iron plate (Figs. 

 It and 10, Plate XLIII), about au inch thick, faced en one side, and provided or not 

 with flanges on each side. It rests on a firm table or timber support. The ore is laid 

 on the plate and ground with the bucker. The bucker (Fig. 11, Plate XLIII) is a mass 

 of cast iron, with a cylindrical lower surface, faced on the plate side, and fixed to a 



